As most electronic equipment including personal computers, digital cameras and mobile phones become of smaller size and better performance, there is an increasing demand for semiconductor devices of small size, thin profile and high density. There is a desire to have a photosensitive dielectric material which can accommodate an increase of substrate area for productivity improvement and which can accommodate structures having fine asperities with a high aspect ratio on substrates in the high-density packaging technology as typified by chip size packages or chip scale packages (CSP) or 3D layer stacks.
With respect to the photosensitive dielectric material mentioned above, JP-A 2008-184571 discloses a photo-curable resin composition which can be coated to form films having a widely varying thickness by the spin coating technique commonly used in the semiconductor device fabrication, processed into fine size patterns using radiation of a wide wavelength range, and post-cured at low temperatures into electric/electronic part-protecting films having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance. Advantageously, the spin coating technique is capable of simply forming a film on a substrate.
The photo-curable resin composition for forming electric/electronic part-protecting films is used to form a film having a thickness of 1 to 100 μm on a substrate. As the film thickness increases beyond 30 μm, it becomes difficult to apply the photo-curable resin composition onto the substrate by spin coating because the composition must have a very high viscosity. The film formation on substrate by spin coating encounters a certain limit in the practical application.
Also, when the photo-curable resin composition is applied onto a substrate having a rugged surface by spin coating, it is difficult to form a uniform layer on the substrate. The photo-curable resin layer tends to leave voids near steps on the substrate. Further improvements in planarity and step coverage are desired. Another coating technique replacing the spin coat technique is spray coating as disclosed in JP-A 2009-200315. Owing to the principle of spraying, defects are often formed including height difference arising from asperities on the substrate, film rupture at pattern edges and pinholes at recess bottom. The problems of planarity and step coverage still remain unsolved.
Recently, in the high-density package technology as typified by chips scale packages (CSP) or 3D stacked packages, a focus is put on the technique of redistribution from chips by forming a fine, high aspect ratio pattern on a substrate and depositing a metal such as copper on the pattern. To meet a demand for chips of higher density and higher integration, it is strongly desired to reduce the width of pattern lines and the size of contact holes for interconnection between substrates in the redistribution technology. The lithography is generally used for forming fine size patterns. In particular, the lithography combined with chemically amplified negative resist compositions is best suited for forming fine pattern features. Since the pattern used for redistribution is permanently left between device chips, the pattern material must have a cure ability and also serve as an electric/electronic part-protecting film having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance. For this reason, a negative resist composition is believed suitable for forming such patterns.
Accordingly, a chemically amplified negative resist composition is typical of the pattern-forming material which can be processed into a fine redistribution layer and serve as an electric/electronic part-protecting film having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance.
On the other hand, the negative resist compositions of current frequent use are required to have resistance to various chemicals as the process of fabricating semiconductor devices after pattern formation becomes complex. In particular, there is a need for a negative resist composition which remains fully resistant to alkaline reagents used for removal of plating over a long period of time.